Abstract
The process can be understood as a combination of a thermal method (steam injection) with a miscible method (solvent injection), promoting, thus, reduction of interfacial tensions and oil viscosity. When co-injected with steam, the vaporized solvent condenses in the cooler regions of the reservoir and mixes with oil, creating a zone of low viscosity between steam and heavy oil. Mobility of the displaced fluid is then improved, resulting in an increase of oil recovery and oil rates. To better understand this improved oil recovery method, a numerical study of the process was done contemplating the effects of some operational parameters (distance between wells, steam injection rate, solvent type and injected solvent volume) on cumulative oil produced and oil rates. Simulations were performed in STARS (CMG, 2007.11).
Semi synthetic model was used in this study and some reservoir data were obtained similar to those found in Brazilian Potiguar Basin. The method presented good performance for heavy oil reservoirs with approximately 200 m depth, porosity between 20% and 30%, vertical/horizontal permeabilities ratio of 10% and thickness around 30 m.
It was found that injected solvent volumes increased oil recovery and oil rates. Further, the majority of the injected solvent was produced and can be recycled. For applications of optimized model with oil viscosities of 300 cP, 1000 cP and 3000 cP, the most important oil recovery was obtained for the lightest one (300 cP), while for 1000 cP and 3000 cP, the final recovery was practically the same.
The high initial productions achieved by models that use solvent as an advanced recovery method have normally a significant impact on the operation economics, because early production suggests that fluids injection (steam and solvent) can be interrupted earlier. On environmental point of view, solvent injection can provide a reduction of energy and also a reduction in water consumptions for steam generation, having diminished Green House Gases (GHG) emissions. Also it is important to emphasize that the higher oil rates presented by these models can generate an earlier financial return and, by consequence, a project with a good economical viability.
